VPAC1 receptor expression in peripheral blood mononuclear cells in a human endotoxemia model

Immune evasion by Salmonella: exploiting the VPAC1/VIP axis in human monocytes

Immune evasion is a critical survival mechanism for bacterial colonization of deeper tissues and may lead to life-threatening conditions such as endotoxaemia and sepsis. Understanding these immune evasion pathways would be an important step for the development of novel anti-microbial therapeutics. Here, we report a hitherto unknown mechanism by which Salmonella exploits an anti-inflammatory pathway in human immune cells to obtain survival advantage. We show that Salmonella enterica serovar Typhimurium strain 4/74 significantly (P < 0·05) increased expression of mRNA and surface protein of the type 1 receptor (VPAC1) for anti-inflammatory vasoactive intestinal peptide (VIP) in human monocytes. However, we also show that S. Typhimurium induced retrograde recycling of VPAC1 from early endosomes to Rab11a-containing sorting endosomes, associated with the Golgi apparatus, and anterograde trafficking via Rab3a and calmodulin 1. Expression of Rab3a and calmodulin 1 were significantly increased by S. Typhimurium infection and W-7 (calmodulin antagonist) decreased VPAC1 expression on the cell membrane while CALP-1 (calmodulin agonist) increased VPAC1 expression (P < 0·05). When infected monocytes were co-cultured with VIP, a significantly higher number of S. Typhimurium were recovered from these monocytes, compared with S. Typhimurium recovered from monocytes cultured only in cell media. We conclude that S. Typhimurium infection exploits host VPAC1/VIP to gain survival advantage in human monocytes.

Immunomodulation by vasoactive intestinal peptide is associated with increased survival and growth of Salmonella Typhimurium in mice

Studies have shown that administration of vasoactive intestinal peptide (VIP) in mice rescues them from lethal endotoxaemia and that this is correlated with decreased concentration of inflammatory cytokines. VIP has, therefore, been proposed as a novel anti-inflammatory which could be used in the treatment of Gram negative sepsis. However, the effect of VIP has not been reported in mice infected with viable Gram negative bacteria. Here, we show that Salmonella enterica serovar Typhimurium 4/74 significantly increased expression of mRNA of a type 1 receptor (VPAC1) for anti-inflammatory vasoactive intestinal peptide (VIP) in murine ileum and mesenteric lymph nodes at day 6 post-infection (d6 pi) and in the spleen at d3 pi. When VIP (5 nmol/ml) was administered to S. Typhimurium-infected mice, there was a significant increase in the number of S. Typhimurium cultured from murine faeces and ileum at d3 and 6 pi and in MLN and spleen at d3 dpi, compared to faeces and tissues examined from mice infected with S. Typhimurium (without VIP administration). Administration of VIP to S. Typhimurium-infected mice also altered the splenic architecture, resulting in a lack of discernable periarterial lymphoid sheaths or marginal zones at d6 pi but liver histology appeared similar on both d3 and d6 pi. The effects of VIP administration were correlated with a significant decrease in expression of inflammatory cytokine mRNA, associated with systemic inflammatory response syndrome (SIRS) of bacteraemia and acute sepsis. We conclude that VIP inhibits expression of diagnostic/prognostic cytokine biomarkers of sepsis in S. Typhimurium-infected mice. However, this occurred with a concomitant increase in Salmonella growth in tissues and increased bacterial shedding in faeces. Thus, VIP may have potential as an adjunctive therapy to antibiotics in sepsis.

An Overview of VPAC Receptors in Rheumatoid Arthritis: Biological Role and Clinical Significance

The axis comprised by the Vasoactive Intestinal Peptide (VIP) and its G protein-coupled receptors (GPCRs), VPAC1, and VPAC2, belong to the B1 family and signal through Gs or Gq proteins. VPAC receptors seem to preferentially interact with Gs in inflammatory cells, rather than Gq, thereby stimulating adenylate cyclase activity. cAMP is able to trigger various downstream pathways, mainly the canonical PKA pathway and the non-canonical cAMP-activated guanine nucleotide exchange factor (EPAC) pathway. Classically, the presence of VPACs has been confined to the plasma membrane; however, VPAC1 location has been described in the nuclear membrane in several cell types such as activated Th cells, where they are also functional. VPAC receptor signaling modulates a number of biological processes by tipping the balance of inflammatory mediators in macrophages and other innate immune cells, modifying the expression of TLRs, and inhibiting MMPs and the expression of adhesion molecules. Receptor signaling also downregulates coagulation factors and acute-phase proteins, promotes Th2 over Th1, stimulates Treg abundance, and finally inhibits a pathogenic Th17 profile. Thus, the VIP axis signaling regulates both the innate and adaptive immune responses in several inflammatory/autoimmune diseases. Rheumatoid arthritis (RA) is a complex autoimmune disease that develops on a substrate of genetically susceptible individuals and under the influence of environmental factors, as well as epigenetic mechanisms. It is a heterogeneous disease with different pathogenic mechanisms and variable clinical forms between patients with the same diagnosis. The knowledge of VIP signaling generated in both animal models and human ex vivo studies can potentially be translated to clinical reality. Most recently, the beneficial effects of nanoparticles of VIP self-associated with sterically stabilized micelles have been reported in a murine model of RA. Another novel research area is beginning to define the receptors as biomarkers in RA, with their expression levels shown to be associated with the activity of the disease and patients-reported impairment. Therefore, VPAC expression together VIP genetic variants could allow patients to be stratified at the beginning of the disease with the purpose of guiding personalized treatment decisions.

Vasoactive intestinal peptide dampens formyl-peptide-induced ROS production and inflammation by targeting a MAPK-p47phox phosphorylation pathway in monocytes

Reactive oxygen species (ROS) produced by the phagocyte NADPH oxidase (NOX2) are required for microbial clearance; however, when produced in excess they exacerbate inflammatory response and injure surrounding tissues. NOX2 is a multicomponent enzyme composed of membrane-associated cytochrome b588 and cytosolic components p47^phox, p67^phox, p40^phox, and rac1/2. We investigated whether vasoactive intestinal peptide (VIP), an endogenous immune-modulatory peptide, could affect ROS production by NOX2 in primary human phagocytes. VIP did not modulate basal ROS production by phagocytes, but it inhibited monocyte and not neutrophil ROS production in response to the bacterial peptide N-formyl-methionyl-leucyl-phenylalanine (fMLF). The action of VIP was essentially mediated by high-affinity G-protein coupled receptors VPAC1 as its specific agonist, [ALA^11,22,28]VIP, mimicked VIP-inhibitory effect, whereas the specific VPAC1 antagonist, PG97-269, blunted VIP action. Further, we showed that VIP inhibited fMLF-induced phosphorylation of ERK1/2 (extracellular signal-regulated kinase 1/2), p38MAPK (p38 mitogen-activated protein kinase) pathways, and phosphorylation of p47^phox on Ser345 residue. Also, VIP exerted an anti-inflammatory effect in a model of carrageenan-induced inflammation in rats. We thus found that VIP exerts anti-inflammatory effects by inhibiting the "MAPK-p47^phox phosphorylation-NOX2 activation" axis. These data suggest that VIP acts as a natural anti-inflammatory agent of the mucosal system and its analogs could be novel anti-inflammatory molecules.

VIP impairs acquisition of the macrophage proinflammatory polarization profile

This study tested the hypothesis that vasoactive intestinal peptide (VIP) is able to modify the macrophage inflammatory profile, thus supporting its therapeutic role in autoimmune diseases. Macrophages are innate immune cells that display a variety of functions and inflammatory profiles in response to the environment that critically controls their polarization. Deregulation between the pro- and anti-inflammatory phenotypes has been involved in different pathologies. Rheumatoid arthritis (RA) is an autoimmune disease, in which macrophages are considered central effectors of synovial inflammation, displaying a proinflammatory profile. VIP is a pleiotropic neuropeptide with proven anti-inflammatory actions. As modulation of the macrophage phenotype has been implicated in the resolution of inflammatory diseases, we evaluated whether VIP is able to modulate human macrophage polarization. In vitro-polarized macrophages by GM-CSF (GM-MØ), with a proinflammatory profile, expressed higher levels of VIP receptors, vasoactive intestinal polypeptide receptors 1 and 2 (VPAC1 and VPAC2, respectively), than macrophages polarized by M-CSF (M-MØ) with anti-inflammatory activities. RA synovial macrophages, according to their GM-CSF-like polarization state, expressed both VPAC1 and VPAC2. In vitro-generated GM-MØ exposed to VIP exhibited an up-regulation of M-MØ gene marker expression, whereas their proinflammatory cytokine profile was reduced in favor of an anti-inflammatory function. Likewise, in GM-MØ, generated in the presence of VIP, VIP somehow changes the macrophages physiology profile to a less-damaging phenotype. Therefore, these results add new value to VIP as an immunomodulatory agent on inflammatory diseases.

VPAC1 receptor (Vipr1)-deficient mice exhibit ameliorated experimental autoimmune encephalomyelitis, with specific deficits in the effector stage

BACKGROUND

Vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase-activating polypeptide (PACAP) are two highly homologous neuropeptides. In vitro and ex vivo experiments repeatedly demonstrate that these peptides exert pronounced immunomodulatory (primarily anti-inflammatory) actions which are mediated by common VPAC1 and VPAC2 G protein-coupled receptors. In agreement, we have shown that mice deficient in PACAP ligand or VPAC2 receptors exhibit exacerbated experimental autoimmune encephalomyelitis (EAE). However, we observed that VIP-deficient mice are unexpectedly resistant to EAE, suggesting a requirement for this peptide at some stage of disease development. Here, we investigated the involvement of VPAC1 in the development of EAE using a VPAC1-deficient mouse model.

METHODS

EAE was induced in wild-type (WT) and VPAC1 knockout (KO) mice using myelin oligodendrocyte glycoprotein 35-55 (MOG35-55), and clinical scores were assessed continuously over 30 days. Immune responses in the spinal cords were determined by histology, real-time PCR and immunofluorescence, and in the draining lymph nodes by antigen-recall assays. The contribution of VPAC1 expression in the immune system to the development of EAE was evaluated by means of adoptive transfer and bone marrow chimera experiments. In other experiments, VPAC1 receptor analogs were given to WT mice.

RESULTS

MOG35-55-induced EAE was ameliorated in VPAC1 KO mice compared to WT mice. The EAE-resistant phenotype of VPAC1 KO mice correlated with reduced central nervous system (CNS) histopathology and cytokine expression in the spinal cord. The immunization phase of EAE appeared to be unimpaired because lymph node cells from EAE-induced VPAC1 KO mice stimulated in vitro with MOG exhibited robust proliferative and Th1/Th17 responses. Moreover, lymph node and spleen cells from KO mice were fully capable of inducing EAE upon transfer to WT recipients. In contrast, WT cells from MOG-immunized mice did not transfer the disease when administered to VPAC1 KO recipients, implicating a defect in the effector phase of the disease. Bone marrow chimera studies suggested that the resistance of VPAC1-deficient mice was only minimally dependent on the expression of this receptor in the immunogenic/hematopoietic compartment. Consistent with this, impaired spinal cord inductions of several chemokine mRNAs were observed in VPAC1 KO mice. Finally, treatment of WT mice with the VPAC1 receptor antagonist PG97-269 before, but not after, EAE induction mimicked the clinical phenotype of VPAC1 KO mice.

CONCLUSIONS

VPAC1 gene loss impairs the development of EAE in part by preventing an upregulation of CNS chemokines and invasion of inflammatory cells into the CNS. Use of VPAC1 antagonists in WT mice prior to EAE induction also support a critical role for VPAC1 signaling for the development of EAE.

Regulation of nutrition-associated receptors in blood monocytes of normal weight and obese humans

Obesity, type 2 diabetes and associated metabolic diseases are characterized by low-grade systemic inflammation which involves interplay of nutrition and monocyte/macrophage functions. We suggested that some factors such as nutrient components, neuropeptides involved in the control of gastrointestinal functions, and gastrointestinal hormones might influence immune cell functions and in this way contribute to the disease pathogenesis. The aim of this study was to investigate the mRNA expression of twelve nutrition-associated receptors in peripheral blood mononuclear cells (PBMC), isolated monocytes and monocyte-derived macrophages and their regulation under the switching from the high-carbohydrate low-fat diet to the low-carbohydrate high-fat (LC/HFD) isocaloric diet in healthy humans. The mRNA expression of receptors for short chain fatty acids (GPR41, GPR43), bile acids (TGR5), incretins (GIPR, GLP1R), cholecystokinin (CCKAR), neuropeptides VIP and PACAP (VIPR1, VIPR2), and neurotensin (NTSR1) was detected in PBMC and monocytes, while GPR41, GPR43, GIPR, TGR5, and VIPR1 were found in macrophages. Correlations of the receptor expression in monocytes with a range of metabolic and inflammatory markers were found. In non-obese subjects, the dietary switch to LC/HFD induced the increase of GPR43 and VIPR1 expression in monocytes. No significant differences of receptor expression between normal weight and moderately obese subjects were found. Our study characterized for the first time the expression pattern of nutrition-associated receptors in human blood monocytes and its dietary-induced changes linking metabolic responses to nutrition with immune functions in health and metabolic diseases.